Han Seong-Tae, Griffin Robert G, Hu Kan-Nian, Joo Chan-Gyu, Joye Colin D, Sirigiri Jagadishwar R, Temkin Richard J, Torrezan Antonio C, Woskov Paul P
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139-4294 USA.
IEEE Trans Plasma Sci IEEE Nucl Plasma Sci Soc. 2007 Jun;35(3):559-564. doi: 10.1109/TPS.2007.896931.
Gyrotrons operating in the millimeter and submillimeter wavelength ranges are the promising sources for applications that are requiring good spectral characteristics and a wide range of output power. We report the precise measurement results of gyrotron spectra. Experiments were conducted using a 140-GHz long-pulse gyrotron that is developed for the dynamic nuclear polarization/nuclear-magnetic-resonance spectroscopy at the Massachusetts Institute of Technology. Transient downshift of the frequency by 12 MHz with a time constant of 3 s was observed. After reaching equilibrium, the frequency was maintained within 1 ppm for over 20 s. The coefficient of the frequency change with cavity temperature was -2.0 MHz/K, which shows that fine tuning of the gyrotron frequency is plausible by cavity-temperature control. Frequency pulling by the beam current was observed, but it was shown to be masked by the downward shift of the gyrotron frequency with temperature. The linewidth was measured to be much less than 1 MHz at 60 dB relative to the carrier power [in decibels relative to carrier (dBc)] and 4.3 MHz at 75 dBc, which is the largest dynamic range to date for the measurement of gyrotron linewidth to our knowledge.
工作在毫米和亚毫米波长范围内的回旋管是那些需要良好光谱特性和宽输出功率范围的应用的有前途的源。我们报告了回旋管光谱的精确测量结果。实验使用了一台为麻省理工学院的动态核极化/核磁共振光谱学开发的140 GHz长脉冲回旋管进行。观察到频率有12 MHz的瞬态下移，时间常数为3 s。达到平衡后，频率在超过20 s的时间内保持在1 ppm以内。频率随腔温度的变化系数为-2.0 MHz/K，这表明通过控制腔温度对回旋管频率进行微调是可行的。观察到了束流引起的频率牵引，但结果表明它被回旋管频率随温度的下移所掩盖。在相对于载波功率为60 dB [相对于载波的分贝数（dBc）]时，测得线宽远小于1 MHz，在75 dBc时为4.3 MHz，据我们所知，这是迄今为止测量回旋管线宽的最大动态范围。
